I. Field of the Invention
The present invention relates generally to underwater dredging and, more particularly, to a system and method for determining the depth of a bucket of the dredging system.
II. Description of Related Art
It is oftentimes necessary to dredge the bottom of a water body, such as a river, lake or the like. For example, in some situations an environmentally dangerous material may be spilled into the water body which must be removed for environmental reasons. In still other circumstances, dredging is conducted merely to increase the depth of the water body.
In order to perform the dredging operation, a power shovel is typically mounted on a barge and the barge is then moved to the desired location on the water body for the dredging operation. In such cases, the horizontal position of the barge can be easily, rapidly and accurately obtained using a GPS system.
During a dredging operation, it is important that the depth of the dredging operation be controlled as accurately as possible or at least within a preset range. For example, in the event that the dredging operation is conducted to remove an environmental hazard at the bottom of the water body, it is important that a sufficient amount of the bottom of the water body be removed in order to ensure the complete or near-complete removal of the environmental hazard.
Conversely, it is also desirable not to dredge the water body more than a specified depth due to the relatively high cost of the dredging operation. This is also particularly true where the dredging operation is conducted to remove an environmental hazard since the removed soil oftentimes must be transported to a special biohazard dump site. Such dump sites typically charge rates tied to the weight of the soil so that the removal of too much soil from the bottom of the water body increases the cost of the disposal of the removed soil.
There are different types of power shovels. For example, in one type of power shovel, a clamshell bucket is suspended on a cable which is positioned by an elevated crane. In this type of power shovel, it is relatively straightforward to determine the vertical position of the bucket within the water body by simply placing a pressure sensor at a predetermined position on the cable above the bucket. Since the vertical spacing between the sensor and the bucket remains constant, the depth of the bucket may be easily determined by simply determining the depth of the sensor and adding the spacing between the sensor and the bucket to that sensor depth.
In other types of power shovels, the power shovel includes a power housing having two articulated manipulator arms extending outwardly from the housing. One end of one arm is coupled to the housing while a bucket is mounted to the free end of the other arm. With this type of power shovel, the position of the bucket, both horizontally as well as vertically, varies with the angular position of the manipulator arms relative to both the power housing as well as each other.
Unlike the previously known cable suspended clamshell buckets, it is not possible to determine the vertical position of the bucket by simply placing a pressure sensor on the manipulator arm above the bucket since the vertical spacing between the sensor and the bucket will vary as a function of the angular position of the manipulator arms. For example, if the outer manipulator arm, i.e. the manipulator arm having the bucket at its free end, is extended outwardly in a generally horizontal direction, the vertical spacing between the sensor and the bucket is relatively small. Conversely, if the outer manipulator arm is generally vertically oriented, then the spacing between the depth sensor and the bucket will be relatively large. Consequently, there are no previously known systems for accurately determining the depth of the power bucket for a power shovel of the type having two or more articulated manipulator arms.